Silicon just like high purity diamond, can conduct electricity when lightly doped n type or p type. That is to say, conduction by electrons or holes. Elements like Boron and Phosphorous as well as others, enter the crystal lattice and replace the Si atoms. Since the dopant atoms are of a different valance state, they produce excess electrons or holes to balance the overall charge. Thaat is to say, we create extrinsic carriers.

Since conductivity depends on 2 things, carrier mobility (how fast the e- or h+ travel), and carrier concentration (how many there are), we just decreased the resistivity to 1/100 of most metallic conductors (pretty darn good, but still pretty high which is why our computers get hot.....lost electrons turn into heat).

Since Si and C both bond to the diamond structure, they are readily dissolved into one another (granted the atmosphere and pressure are right). In doing so, the electronic configuration is slightly altered due to the 2 different elements in coordination with one another. Where the silicon band gap is around 1.2 eV, SiC has a band gap of around 2 - 3 eV. The band gap is the energy required (the potenial in Volts) to promote electrons from the valence band to the conduction band.

So basically it becomes a little harder to accomplish this, however the thermal conductivity of SiC is 20 times greater, which means better heat disspation. Si is around 17 Wm/K where SiC is 300 W/mK (300 depending on how its processed and which crystal direction as its anisotropic). Copper is around 500, gold around 300, Silver 400, and Diamond is 4000! the best thermal conductor by far because of the extremely strong C-C bonds.

The final problem may be a little complicated. I'm guessing what your asking is because of the intrinsic carriers. These are thermally induced naturally occuring e- or h+. Silicon begins producing large amounts of intrinsic deffects above 100C. This is why your computer dies above that temperature. The whole substrate becomes conductive and it shorts itself. Intrinsic carrier concentration, and the ability to produce them is related to the band gap. The smaller the band gap, the less energy needed to jump bands, therefore the more carriers produced by heating.

Don't understand well... How can the Boron atoms jack into the Silicon's complicated diamond structures?

Thats why only a small atomic percentage is used. Actually, the most expensive diamonds contain more boron. It increases the hardness by inducing stress/strain in the crystal from the mismatch in atomic radii.

That means Boron is originally inside them in order to make them better....!?

Fundamentally,
the reason you're confused, Deryck, is when you say "I think covalent bonds cannot conduct electricity?"

What you must remember is that all these notions about electrons and bonds and so forth is just a lot of made-up theoretical nonsense lol

Whilst it is often useful to consider covalent bonds as localised shared pairs of electrons, which sit in a single place,
this doesn't do much to explain how a semiconductor or a metal conduct electricity.

To explain this, we tend to use a whole new made-up theory, "BAND THEORY", which looks at large-scale bonding in the solid state.
It takes a quantum mechanical approach, and takes all the orbitals for each atom, and merges them into huge enormous "bands" of orbitals which stretch throught the entire bulk solid (well, across each crystal).
Some bands are full and the electrons can't swim around in them .... metals and semiconductors have various empty or sparsely populated bands where the electrons are free to conduct (heat, and electricity)
This can also explain things about why copper and gold are nice colours, why some metals are shinier than others, and so on....

That is, you mean, Silicon atoms share electrons through covalent bonds, and the electrons shared through the bonds merge and transmit electrivity?

Well, sort of -)

Don't think of a "bond" or an "orbital" and a container that has the electrons "inside" it..... think electrons *are* the bond (or the orbital), vibrating in a particular shape and space.

Remember that the atomic nuclei are ABSOLUTELY TINY compared to the clouds of electrons which orbit them.

If the atom was a big football stadium, then the nucleus would probably be the size of a single football in the middle.

It is not generally useful to think of electrons as little particules. When bound in atoms or molecules, try to think of them as vibrating waves of negative charge.
The shape of these vibrating waves are the shapes of the orbitals (s, p, d, f....)

In molecules, the atomic orbitals merge into new vibrating shapes
(perhaps you have heard of sigma & pi & delta orbitals in simple molecule?)

In a large-scale solid lattice (like a lump of silicon), you therefore have tiny tiny dots of nuclei in there, surrounded mostly by vast empty spaces in between.
In these lonely open spaces, great shimmering masses of vibrating negative charge swoosh and pulse around.
These vibrating waves have merged into big ripples that reach through the entire solid lattice - it no longer useful to think of them as localised in "bonds" of electron pairs, pointing in tetrahedrons around each silicon.

In a semiconductor, there will be "holes" in the huge shimmering negative charge wave (where there are electrons "missing") and these holes can move around - this is conducting electricity

Aren't the Silicon atoms held up tightly with each other? How can there be vacancies in the waves? (electron missing? there shouldn't be if it's chemically stable.)

The entire lattice is strongly bound, yes, spread throughout in 3 dimensions. The electrons glue the whole thing together.

There will be a "hole" in the wave if one of the silicons is replaced with a gallium (Group III) , for instance (this is called "doping")... if a group V atom was doped in (Arsenic?) then you'd have an extra electron sloshing about inside the lattice. It would have to occupy a higher energy orbital band (ie, vibrate in a more antibonding pattern)

Imagine it like seawater waves swirling up a rocky beach there will be big wavefront shapes reaching for hundreds of yards across, but around particular rocks, there maybe be little "holes" (swirls and eddies)in the wave shapes, which roll and move about as the waves sweep by.

That is, impurity makes the silicon conductive....? Then why do people make pure silicon?